The invention relates to a multi-component measuring disc wheel for vehicles. Such a measuring disc wheel is known, for example, from a public lecture on the subject "Multi-component measuring technology" given by U. Schafer on 21 Feb. 1990 in the Haus der Technik in Essen (DE) wherein each member of the audience was given a copy of the lecture manuscript, including the illustrative part. The lecture was given as part of an entire day lecture meeting which included a total of nine new lectures on the general subject of "Measurements using test vehicles."
In addition to the multi-component measuring disc wheel, the above-cited lecture also deals with older measuring devices for the same purpose. Specially designed stub axles or wheel supports have previously, in fact, been installed for measuring purposes. Apart from the complicated conversion measures preceding a measurement and the fact that the measurement capability is limited to a single vehicle, the measurement stub axles have the disadvantage that they cannot measure braking forces so that a separate measuring device must be provided for these forces. Another, older type of measuring device is represented by the multi-component measuring hubs known in several different forms (see, for example, German Patent Document 21 04 003). These measuring hubs do not rotate with the vehicle wheel and--like the measuring stub axles--require special parts within the axle construction of the measuring vehicle. Complicated conversion of the vehicle was also, therefore, necessary prior to measurement when using multi-component measuring hubs.
So-called multi-component measuring disc wheels, integrated in a vehicle wheel, with rotating measuring devices for this purpose leave the whole of the axle construction of the vehicle unaffected and can therefore be used on different vehicles without substantial conversion measures. Because of this fundamental advantage, multi-component measuring disc wheels have been proposed by various parties. The measurement sensitive part of the multi-component measuring disc wheel shown in German Patent Document 23 02 540 has two rings at an axial distance from one another, each with four radially extending and peripherally evenly spaced measuring webs through which the force flow passes from the tire to the wheel hub and which have strain gauges applied to them. German Patent Document 28 28 538 shows a similar multi-component measuring disc wheel in which eight measuring webs are provided for each measuring web ring. The way in which the individual force components of interest are isolated by measurement techniques is not apparent from these publications. In addition, these multi-component measuring disc wheels are very voluminous and heavy and, for this reason, are not suitable for exacting measurements because, due to the additional masses, the forces to be measured are changed in a manner which is not negligible compared to a similar vehicle without a multi-component measuring disc wheel.
The measurement-sensitive part of the multi-component measuring disc wheel known from German Patent Document 32 13 319 provides, for certain fundamental measurement technology considerations, four radially weak locations on the periphery of the measurement-sensitive part. Because the multi-component measuring disc wheel is held by means of this part and the whole of the force flow is guided through this part, the stiffness of the known multi-component measuring disc wheel is impaired relative to a normal vehicle wheel and this falsifies the force relationships relative to travel with a normal wheel and, therefore, the representative nature of the measurement relative to such a driving operation.
European Laid-Open Application 352 788 shows a further multi-component measuring disc wheel which is very complicated in design; it is also very heavy, simply because of the many bolted connections, so that additional masses which falsify the measurement are to be expected. The mutual separation by measurement techniques of the measurement signals for the individual components is produced in this case by providing several different force flow paths which are made weak by an appropriate arrangement of links or flexible features relative to the respective loads which are not intended for them. Apart from the weight- the known multi-component measuring disc wheel does not therefore agree with a conventional vehicle wheel with respect to stiffness too.
The multi-component measuring disc wheel based on the generic type in accordance with the literature reference quoted at the beginning is very simple in construction and can also be made correspondingly stiff and light so that, at least if appropriate use is made of lightweight measures--use of high-strength lightweight structural materials and the application of mass-reducing recesses at the less loaded locations--a mass and stiffness corresponding to the normal wheel with respect to translational and rotational accelerations and loads can be achieved. Although the literature reference mentions that a good measurement signal resolution is possible with the multi-component measuring disc wheel, with little cross-coupling between the individual components, it does not deal with the question of how this is achieved. In connection with the calculation of the forces actually acting from the initially recorded measurement signals, however, the reference indicates that a system of four equations with four unknowns has to be solved continually in real-time in order to be able to determine the forces actually acting and of interest. In addition, complicated calibrations have to be undertaken and these must be taken into account in the calculation. From this, it may be concluded that the multi-component measuring disc wheel based on the generic type is complicated and expensive with respect to the measurement signal evaluation, which is a hindrance to the easy use of the known multi-component measuring disc wheels.
German Patent Specification 27 08 484 or German Patent Document 28 56 453 show torque measuring discs which can be integrated in the wheel for the isolated measurement of driving torques. In these discs, therefore, other forces or moments acting on the vehicle wheel have to be suppressed. In contrast, however, an attempt is made in the case of the multi-component measuring disc wheels to record several components simultaneously and isolated from one another.
The object of the invention is to improve the multi-component measuring disc wheel--based on the generic type, which is advantageous in many respects, and while retaining its advantages--in such a way that the primarily obtained measurement signals can be converted into the forces actually of interest with relatively small computational effort.
This object is achieved according to the invention by a multi-component measuring disc wheel for vehicles having a rim ring carrying the vehicle tire and an angle-section ring fastened in it instead of a conventional wheel disc. The angle-section ring has an auxiliary flange which is at right angles to the axis and is located axially approximately at the position of the rim flange of the rim ring facing away from the vehicle and whose inner edge has a larger diameter than an envelope circle around the wheel fastening bolts. The disc wheel further has an annular measuring disc held, by means of a plurality of stud bolts parallel to the axis and circular in cross-section, at a distance from the auxiliary flange on the side of the multi-component measuring disc wheel facing away from the vehicle. The inner edge of the measuring disc has a smaller diameter than the inner edge of the auxiliary flange but again having a larger diameter than the envelope circle around the wheel fastening bolts.
Stud bolts, which are designed to be identical to one another apart from very small tolerances, act as axial measuring cross-sections and are equipped with strain gauges. They are evenly distributed on a common pitch circle and are fastened in a torsionally stiff manner both in the measuring disc and in the auxiliary flange and are additionally positively secured against rotation.
The measuring disc has a number of radially extending, spoke-type measuring webs which can be divided by four without remainder, which measuring webs extend between an outer ring closed in the peripheral direction and a closed inner ring and are designed to be identical to one another apart from very small tolerances and again are equipped with strain gauges.
The multi-component measuring disc wheel also has a pot-shaped wheel adaptor bolted axially to the inner edge of the measuring disc, which wheel adaptor compensates for the axial distance between the measuring disc and the normal axial position of the bolt-on flange of the wheel disc of a conventional vehicle wheel and matches in the bolt-on region the bolt-on flange of a conventional vehicle wheel disc.
The measuring disc wheel, has, furthermore, a rotating to stationary signal transmission device at least partially within the pot-shaped wheel adaptor or arranged on it and rotatably mounted in or on the wheel adaptor and a rotational position sensor for the multi-component measuring disc wheel. The stationary par of the signal transmission device and of the rotational position sensor is fixed in a defined position on the vehicle body in the rotational direction of the multi-component measuring disc wheel by means of a linkage compensating for the suspension and/or steering motions of the multi-component measuring disc wheel.
The strain gauges applied to the axial stud bolts and the radial measuring webs are applied in such a position in each case and with respect to their alignment and are connected into associated electrical measuring bridge circuits in such a way that isolated electrical signals can be obtained with respect to the following components, i.e.
1) the vertically directed wheel load extending radially through the wheel center;
2) the horizontally directed longitudinal force, again extending radially through the wheel center;
3) the eccentric side force acting on the wheel contact surface and directed transversely to the plane of the wheel; and
4) the eccentric braking force directed parallel to the rolling direction of the vehicle wheel, i.e. acting tangentially at the wheel contact surface.
The interaction of the following features is as follows. The radially extending measuring webs of the measuring disc are used for determining the forces acting eccentrically at the wheel contact surface of the multi-component measuring disc wheel, i.e. the braking force (BK) and the side force (SK) and, for this purpose and for mutual elimination by measurement techniques, are equipped in two different ways with strain gauges whereby, for the isolated recording of the braking force directed parallel to the plane of the wheel, the peripheral bending load on the measuring webs is determined and, in consequence, strain gauges are applied in each case to the two flat sides opposite to one another in the peripheral direction of at least some of the measuring webs at the radial position of maximum bending load. The strain gauges are aligned with their measurement sensitivity parallel to the side edges and the measuring webs selected for this purpose being evenly distributed over the periphery of the measuring disc.
For the isolated recording of the side force (SK) directed transversely to the plane of the wheel, the axial shear load on the measuring webs is determined. In consequence, shear strain gauges are applied in each case to the two flat sides opposite to one another in the peripheral direction of all the measuring webs. The shear strain gauges are arranged crosswise and extending with their measurement sensitivity at an angle of 45.degree. to the side lines.
The axial stud bolts are used for determining a total resultant of the components directed parallel to the plane of the wheel, namely the vertical wheel load (RL), the horizontal longitudinal force (LK) and the braking force (BK). It is possible to resolve the total resultant into its vertical component corresponding to the wheel load (RL) and into its horizontal component corresponding in magnitude to the sum of the longitudinal force (LK) and the known braking force (BK) so that the wheel load (RL) and the longitudinal force (LK) can be determined.
For the elimination by measurement techniques of the effect of the side force (SK) and of the torque effect of the braking force (BK), all the stud bolts are equipped with shear strain gauges in a non-axisymmetrical manner at four peripheral regions which have the same cartesian location in each case--referred to a selected peripheral position of the multi-component measuring disc wheel which can be continually detected by means of the rotational position sensor, it being possible to determine the total resultant quoted in terms of magnitude and--referred to the selected peripheral position--radial direction by means of these shear strain gauges.
The torques acting on the multi-component measuring disc wheel due to the braking forces can be recorded reliably and in an isolated manner by means of a simple measurement of the peripheral bending of the measuring webs. The influence of the side force can be reliably eliminated by the use of the axially aligned stud bolts to measure a total component located parallel to the plane of the wheel and composed of wheel load, longitudinal force and braking force. This is done by measuring the shear load on the stud bolts in association with simultaneous measurement at all the stud bolts. Because of the non-axisymmetrical application of the shear strain gauges, the direction of the total resultant relative to the selected peripheral direction can also be determined without difficulty. The vectorial resolution of this total resultant into a vertical component corresponding to the wheel load and into a horizontal component corresponding in magnitude to the scalar sum of the braking force and the longitudinal force does not represent any computational problem or effort either, so that the signals for these two force components can be provided by only small means which can still be integrated in the signal transmission device. In further processing, it is only necessary to subtract the known braking force from the horizontal component determined in such a manner. The side force can be recorded reliably and without cross-coupling involving other forces by determining the shear load on the measuring webs in the axial direction. In this case, the simultaneous use of all the measuring webs is important to eliminate a load which is non-axisymmetrical in this respect, especially one of different origin.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.